The present invention is directed to a process of hydrogenating nitroalcohols to form aminoalcohols using a homogeneous catalyst system.
The products formed by the present process, aminoalcohols, are known to be useful as disinfectants, lubricating oil additives, textile resin catalysts, buffers and as intermediates in the production of pharmaceutical agents.
It has been known that nitro hydroxyl compounds can be hydrogenated to provide the corresponding amino hydroxyl compounds under certain conditions. In general, the present processes provide for the contacting of a nitroalcohol with a hydrogenation catalyst in a liquid medium. The materials are contained in a suitable apparatus to which hydrogen gas is introduced under pressure. The hydrogenation catalysts deemed suitable for this process are heterogeneous formulations of a Group VII-B or VIII metal. Such materials include porous or spongy metal material such as spongy nickel or Raney nickel or a supported metal or metal compound wherein the catalytically active Group VII-B or VIII metal forms a minor component of the catalyst and is distributed on a variety of inert support materials. Heterogeneous catalysts in many instances provide acceptable initial activity and mechanical strength but are known to rapidly loose their activity and, in the case of supported materials, to soften and disintegrate thereby making heterogeneous catalyst systems unattractive for commercial size operations.
Homogeneous catalyst systems have been used in the reduction of nitroparaffins (see J. F. Knifton article in J. Org. Chem. 40 519-20). In the reduction of nitro compounds, Knifton teaches that a strong base must be present to activate the catalyst complex or the catalyst activity would be so low as to require high catalyst loading and, even then, to achieve low yields. The use of a homogeneous catalyst to reduce nitroparaffins and nitroaromatics has also been reported by Asish Bose et al. in Chemistry & Industry 199 (1987). Bose et al. teach that this homogeneous catalyst system requires the use of a coordination compound. It is well known that hydroxyl groups will decompose and in certain instances cause the nitro alcohol substrate to disintegrate when in the presence of base or coordination compounds as are taught necessary. The systems of Knifton and Bose et al. are, therefore, not applicable to reduction of nitro hydroxyl compounds to which the present invention is directed.
A homogeneous catalyst system is desired to provide effective reduction of nitroalcohols to aminoalcohols.